Lower molecular weight alcohols and ethers such as isopropanol (IPA) and diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have high blending octane numbers. In addition, by-product propylene from which IPA and DIPE can be made is usually available in a fuels refinery. An important aspect of research in the petroleum industry relates to processes to produce high octane lower aliphatic alkyl ethers as octane boosters and supplementary fuels.
The catalytic hydration of olefins, particularly C.sub.3 and C.sub.4 olefins, to provide alcohols and ethers is a well-established art. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,262,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,848; 3,989,762, among others. U.S. Pat. No. 4,886,918 to Sorensen et al. disclosing olefin hydration and etherification to produce DIPE and isopropanol (IPA) is incorporated herein by reference.
Olefin hydration employing medium pore and large pore zeolite catalyst is a known synthesis method. As disclosed in U.S. Pat. No. 4,214,107 (Chang et al.), lower olefins, in particular propylene, are catalytically hydrated over a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of from 1 to 12, e.g., acidic ZSM-5 type zeolite, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product. Acid resin catalysts such as "Amberlyst 15" may also be used for hydration of light olefins.
The production of ether from secondary alcohols such as isopropanol and light olefins is known. As disclosed in U.S. Pat. No. 4,182,914, DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cationic exchange resin as catalyst. Recently, processes for the hydration of olefins to provide alcohols and ethers using zeolite catalyst such as ZSM-5 or zeolite Beta have been disclosed in U.S. Pat. Nos. 4,214,107 and 4,499,313 to Bell et al.; and U.S. Pat. Nos. 4,757,664, 4,857,664 and 4,906,187 to T. Huang. These patents are incorporated herein in their entirety by reference.
In the conversion of a water feedstream and a C.sub.3 hydrocarbons feedstream comprising propene and propane to DIPE and IPA as conventionally practiced, the conversion per pass is about 60%. The reaction effluent is a mixture containing unreacted water, C.sub.3 hydrocarbons and hydrocarbon oligomeric by-products, in addition to the DIPE and IPA products. Separating these components requires multiple distillation and extraction operations that represent a substantial part of the overall process costs. C.sub.3 and any lower hydrocarbons present are effectively removed by distillation and propene is recycled to the high pressure hydration and etherification zone. However, separation of DIPE and IPA is accomplished by an aqueous extraction operation that requires a further distillation step to separate water and IPA/water azeotrope.
The need to separate and recycle propene to the high pressure DIPE reaction zone imposes severe economic burdens on the overall DIPE process, particularly due to the cost associated with splitting the C.sub.3 recycle stream containing unconverted propene. While it is known that zeolite catalyst such as zeolite Beta can achieve very high per pass conversion of propene to DIPE and, theoretically at least, sharply reduce propene recycle, that achievement results in unacceptably high rates for catalyst deactivation. High mol ratios of water to propene are required for the acidic zeolite catalyzed hydration step to achieve high propene conversion to IPA. Under reaction conditions, these levels of excess water result in a hydrothermal attack on zeolite and more rapid catalyst deactivation. Thus, zeolite's advantage vis-a-vis high propene conversion to DIPE are sharply compromised by a more rapid catalyst deactivation in the presence of the large excesses of water required for high propene conversion in the hydration step of the overall reaction.
It is an object of the present invention to provide a process for the production of DIPE having lower operating cost and capital cost.
A further object of the present invention is to provide a process for DIPE production with high propene conversion without recycling unconverted propene.
Another object of the present invention is to provide a once through process, based on propene, for DIPE production at high propene conversion employing zeolite catalyst.